Jan 19 (Reuters) - After months of threatening to undo the Iran nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), Donald Trump once again opted to extend the deal by waiving economic sanctions on Iran. This was the "last chance," he declared in a Jan. 12 statement, "to either fix the deal´s disastrous flaws, or the United States will withdraw."

The U.S. president provided four conditions for a "supplemental agreement" to the JCPOA and called on Congress to ordain them into law. These include: Iran allowing "immediate" inspections of "all sites requested by international inspectors," Iran never coming "close to possessing a nuclear weapon," that there be "no expiration date" for these provisions, and finally, that the legislation explicitly state that Iran´s "long-range missile and nuclear weapons programs are inseparable."

In the event that Congress or American allies in Europe fail to support the so-called supplemental agreement, Trump proclaimed, he would unilaterally "terminate" the JCPOA. This is a shocking attitude towards the European Union member countries, among others.

The reality is that the JCPOA´s text stipulates the highest standards on nuclear transparency and inspections ever negotiated and provides verifiable assurances that Iran´s nuclear program cannot be diverted towards developing nuclear weapons. These measures already meet the first two of Trump´s conditions and surpass anything agreed to by a member of the nuclear non-proliferation treaty (NPT).

Furthermore, while the JCPOA´s major restrictions are temporary, with expiration dates ranging from eight to 25 years, after the deal expires, Iran returns to monitoring under the International Atomic Energy Agency´s "Additional Protocol" safeguards. As noted by more than 90 nuclear scientists in an October 2017 letter supporting the JCPOA, these represent the "strongest set of generally applicable safeguards implemented by the IAEA."

Trump´s conditions seemingly seek to make permanent the JCPOA´s major restrictions on Iran´s nuclear program and connect the Iranian nuclear program to its missile program, despite the opposition of other world powers to any renegotiation of the deal and the conditions representing an egregious violation of the NPT. Indeed, Iran has a sovereign right to enrich uranium for peaceful purposes under the treaty, which states that there should be no discrimination in the right of signatories to benefit from peaceful nuclear technologies and in no way limits states´ abilities to develop conventional weapons.

Iran also has a sovereign right to possess missiles to defend itself. There are no international treaties banning conventional missiles. "President Trump has no right to dictate limits or restrictions over and beyond those just described," said Peter Jenkins, a former UK ambassador to the IAEA.

If Trump follows through with his ultimatum and chooses to leave the JCPOA, his decision will have long-term consequences not only for the United States but also for global attempts to control nuclear proliferation.

First, in the domestic arena, all vital political organs from Congress to Trump´s own national security agencies, including the National Security Council, Pentagon, State Department, and Department of Energy, oppose unilateral American withdrawal because they believe the agreement prevents Iran from developing nuclear weapons and that withdrawal will isolate the United States internationally.

Second, scuttling the JCPOA will increase global mistrust of the United States and remove any incentive for North Korea to negotiate a deal to curtail its own nuclear program. Washington could also find it harder to win support for any military campaign it may launch against Pyongyang if U.S. allies hold it responsible for re-igniting the Iranian nuclear crisis.

Third, the JCPOA was endorsed by the UN Security Council - which includes the United States - and its other members continue to support the deal. Based on the UN charter, it is the obligation of all members to enact Security Council resolutions. Outright U.S. violation of UNSC Resolution 2231 will damage the credibility of other Security Council resolutions and be seen by other member states as hurting its consensus-driven model.

Fourth, the IAEA has on numerous occasions confirmed Iran´s adherence to the deal and has emphasized that U.S. withdrawal will foment a crisis in the agency´s ability to carry out its inspection duties. The JCPOA represents a major achievement for the IAEA because it is the most comprehensive non-proliferation agreement in history. It is a new standard for resolving nuclear crises and its tenets may even have prevented countries such as North Korea from developing nuclear weapons in the first place.

Fifth, the majority of Washington´s allies, including the EU, Japan, Australia, Canada, and South Korea, strongly oppose the United States abandoning the JCPOA. This represents a significant break in America´s alliance system and, going forward, could affect future collaboration on issues such as Russia´s annexation of Crimea.

These factors are presumably the reason Trump has again waived sanctions on Iran. But they will still exist in mid-May - the next deadline for Trump´s sanctions decision - and for every 120 days after that.

Trump´s quest to sabotage the Iran deal is in line with his broader antipathy for Barack Obama´s policies. However, rather than challenging his predecessor´s legacy Trump should endeavor to use it as a model to bolster multilateral diplomacy and resolve crises in places such as Yemen, Syria, and Afghanistan. Today more than ever, the world needs a balanced and rational White House to promote peace and security rather than to flout international norms.

If Trump´s mantra of "America first" means undermining the rules and will of the international community, it will ultimately result in American interests being taken into account last in global decision-making bodies. On the other hand, Trump still has the opportunity to recognize that facilitating the JCPOA is a chance to help burnish his own legacy too. (Reporting by Seyed Hossein Mousavian)